Algebraic Laws
•Laws
involving projections
– PM(R S) = PN(PP(R)
PQ(S))
•Where
N, P, Q are appropriate subsets of attributes of M
– PM(PN(R)) = PM,N(R)
•Example
R(A,B,C,D), S(E, F, G)
– PA,B,G(R S) = P ? (P?(R) P?(S))
D=E
D=E